diff --git a/docs/conf.py b/docs/conf.py
index 34966c2d0..c82f0849b 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -338,16 +338,21 @@ def get_minor_version(package_name: str) -> str:
     "https://suchung.web.cern.ch",
 ]
 
+
 # Settings for myst_nb
+def get_execution_mode() -> str:
+    if "FORCE_EXECUTE_NB" in os.environ:
+        print("\033[93;1mWill run ALL Jupyter notebooks!\033[0m")
+        return "force"
+    if "EXECUTE_NB" in os.environ:
+        return "cache"
+    return "off"
+
+
+nb_execution_mode = get_execution_mode()
 nb_execution_timeout = -1
 nb_output_stderr = "remove"
-
-nb_execution_mode = "off"
-EXECUTE_NB = False
-if "EXECUTE_NB" in os.environ:
-    print("\033[93;1mWill run Jupyter notebooks!\033[0m")
-    EXECUTE_NB = True
-    nb_execution_mode = "cache"
+EXECUTE_NB = nb_execution_mode != "off"
 
 # Settings for myst-parser
 myst_enable_extensions = [
diff --git a/src/ampform/helicity/__init__.py b/src/ampform/helicity/__init__.py
index 398e77cd4..642524e3d 100644
--- a/src/ampform/helicity/__init__.py
+++ b/src/ampform/helicity/__init__.py
@@ -540,7 +540,7 @@ def __generate_helicity_coupling(
 
     def __generate_amplitude_prefactor(
         self, transition: StateTransition
-    ) -> float | None:
+    ) -> sp.Rational | None:
         prefactor = get_prefactor(transition)
         if prefactor != 1.0:
             for node_id in transition.topology.nodes:
@@ -552,7 +552,7 @@ def __generate_amplitude_prefactor(
                         raw_suffix
                     ]
                     if coefficient_suffix != raw_suffix:
-                        return prefactor
+                        return sp.Rational(prefactor)
         return None
 
 
diff --git a/tox.ini b/tox.ini
index db350826b..330bed006 100644
--- a/tox.ini
+++ b/tox.ini
@@ -100,6 +100,20 @@ commands =
     -b html \
     docs/ docs/_build/html
 
+[testenv:docnb-force]
+description =
+  Execute ALL Jupyter notebooks and build documentation with Sphinx
+allowlist_externals =
+  sphinx-build
+passenv =
+  READTHEDOCS_VERSION
+  TERM
+setenv =
+  FORCE_EXECUTE_NB = yes
+  PYTHONHASHSEED = 0
+commands =
+  sphinx-build -nW --keep-going -b html docs/ docs/_build/html
+
 [testenv:jcache]
 description =
   Inspect Jupyter cache